Landing gear fairings reduce drag at these junctions.
Flap track fairings
Fairings are needed to enclose the flap operating mechanism when the flap is up. They open up as the flap comes down and may also pivot to allow the necessary sideways movement of the extending mechanism which occurs on swept-wing installations.
Wing roots are often faired to reduce interference drag between the wing and the fuselage. On top and below the wing it consists of small rounded edge to reduce the surface and such friction drag. At the leading and trailing edge it consists of much larger taper and smooths out the pressure differences: high pressure at the leading and trailing edge, low pressure on top of the wing and around the fuselage.
Wing tips are often formed as complex shapes to reduce vortex generation and so also drag, especially at low speed.
Wheels on fixed gear aircraft
Wheel fairings are often called "wheel pants", "speed fairings" in North America or "wheel spats" or "trousers", in the United Kingdom, the latter enclosing both the wheel and landing gear leg. These fairings are a trade-off in advantages, as they increase the frontal and surface area, but also provide a smooth surface and a faired nose and tail for laminar flow, in an attempt to reduce the turbulence created by the round wheel and its associated gear legs and brakes. They also serve the important function of preventing mud and stones from being thrown upwards against the wings or fuselage, or into the propeller on a pusher craft.
^Molland, Anthony F. and Turnock, Stephen R.:"Marine Rudders and Control Surfaces: Principles, Data, Design and Applications" 1st Edition, section 22.214.171.124. Butterworth-Heineman, 2007. ISBN978-0-75-066944-3